Renewable energy has been in the epicenter interests of energy policy makers in the recent years. However, some forms of renewable energy have received more attention than others. For example, solar, wind and geothermal energy have been in the “spot light”, leaving ocean wave energy behind. This is because the ocean wave energy industry has not yet been able to demonstrate a wave energy converter that overcomes the fundamental challenges being encountered by the existing devices, in order for ocean wave energy to be considered as a reliable renewable energy source. Existing ocean wave energy technologies need to address serious obstacles, which create vital barriers in their commercialization, such as:
(a) very large geometric size of the devices, which leads to high costs,
(b) difficulty of accessing the devices, which makes very costly their corrective and preventive maintenance,
(c) high cost of subcomponents due to non-conventional materials in use for underwater operation,
(d) high risks of operating these devices in harsh ocean conditions, which may lead to a short life-cycles,
(e) low overall efficiency, due to the fact that in most of the devices, the useful electricity finally available after being processed for quality standards (grid quality), is many times less than the electricity initially produced by the converter,
(f) high cost/kilowatt produced due to high device construction costs.
Therefore, there is a need for an ocean wave energy converter having a reasonable size for a significant electricity output of acceptable quality standards, providing easy access for maintenance, made out of conventional components, operating without risk in harsh ocean conditions thus achieving long device life-cycles.
To utilize conventional subcomponents and have easy access for maintenance, ocean wave power transmission, at the most part, needs to take place out of the water. This is achievable with the use of a lever, which has as an input force, the buoyancy force exerted by the waves on a float, attached on the lever, and the float's weight.
In the present invention, a float is attached to the lever's end facing the ocean water. The lever is used to transform the ocean wave energy to mechanical energy, which then can be used for several purposes such as electricity production by using a generator for the electricity grid or local use, or energy storage, for example in the form of a compressed gas in a tank, or thermal energy. Although due to the principle of energy conservation the output energy of a lever is equal to the input energy, still they provide the mechanical advantage of multiplying the input force. Mechanical advantage is only provided by levers of Class 1 or 2. Class 1 levers have the input force (the effort) in the one end, the fulcrum in the middle, and the load in the other end. The force closest to the fulcrum, although it moves a shorter distance, is greater and creates the mechanical advantage generated by the lever. Class 2 levers have the input force in the one end again, the load in the middle and the fulcrum at the other end. They also provide mechanical advantage. Levers of Class 3 have the input force (the effort) in the middle and they do not provide mechanical advantage. A wrench provides mechanical advantage and can be thought as a synthesis of Class 1 and Class 2 levers, having the input force (the effort) in the one end of the wrench and the point that does not move, the fulcrum, proximate to the other end. Class 1 or 2 levers can be used to overcome heavier loads, such as the torque of a high power output generator, or the pressure (PSI) of a tank already containing a substantial mass of a compressed gas etc.
The renewable energy industry is striving to produce higher power output, in order to contribute significantly in today's energy needs. Existing ocean wave energy devices have very large geometric sizes in order to provide with significant energy. The large size is needed to overcome a substantial load, for example a very large torque of a generator or a large resistance force of a pump. The use of a Class 1, or 2, lever can provide with the large forces needed to overcome a large torque or a large resistance force.
Another advantage of using a lever is that it can make possible to convert ocean wave energy into a usable energy by using only solid mechanical parts for power transmission and without involving hydraulic linkages, utilizing pistons and fluids. Mechanical power transmission, using only mechanical components, is simpler and has less power losses than involving hydraulic linkages. If a mechanical energy, generated by a prime mover such as a float, is converted into fluid flow in the process of its conversion into usable energy, it suffers more losses, due to leakages, than if solid mechanical components were used instead.
Another broad aspect of the present invention is a novel device used for (i) protecting a heaving-float-based ocean wave energy converter from harsh conditions and (ii) providing to it a more standardized environment of operation versus the unpredictable nature of the waves. The device is a caisson-like structure, secured in position at the seabed. The structure allows the ocean water to enter and exit from it through an at least one opening on its side walls. The side walls extend higher than the highest wave, and the at least one opening's uppermost point is as at most as high as the height of the lowest wave. The ocean water creates an oscillating water column inside the structure, due to the principle of the connected vessels.
U.S. Patent Application No. 2009/0021017 describes a wave power apparatus which includes a plurality of rotationally supported arms, each of which carries a float at its free end so that a translational movement of the float caused by a wave, results in rotation of the arm. The electricity is produced by using a hydraulic motor and a hydraulic medium.
U.S. Pat. No. 4,203,294 describes a buoy, at least partially submerged in the sea, containing a hydraulic cylinder and piston device, where the piston is fixed to a wire connected to the seabed. The buoy may be kept in a fixed vertical position, by locking the piston to the cylinder by a brake or a valve, thus controlling the rotational movement of an electric generator, through at least one fluid under controlled circulation within the water displacing member.
U.S. Patent Application No. 2011/0030365 discloses an energy production system comprising at least one liquid reservoir having a predetermined arrangement of inlet and outlet to provide periodically changes in a liquid level, at least one float, at least partially immersed in liquid within the liquid reservoir, a lock system and a controller. The mechanical power produced by the vertical motion of the float, may be transformed to electrical power by using a generator, which is attached to the float.
The intermittencies of renewable sources have created a need for energy storage and release, when energy is demanded. Energy storage can provide a solution to the renewable energy intermittencies. In addition, electric energy storage, produced by a renewable energy converter, may increase the converter's overall efficiency. This is because the electricity initially produced by most renewable energy converters, requires further processing, mainly through costly power electronics, in order to become usable. During this processing though, a substantial quantity of electric power is lost. For example, most of wave energy converters, due to the variability of the heights and frequencies of the waves, initially produce not-usable electricity or electricity of grid quality. This electricity requires further processing, to become usable. The quantity, though, of the finally produced usable electricity is less than the quantity of the initially generated not-usable electricity. Therefore, if there was a way to store this initially produced, not-usable energy, in an energy storage device, and retrieve it later as usable electricity, with the reasonable loses of the retrieval process, we would achieve on-demand energy from the renewable source. The present teaching describes two novel methods of such energy storage. Both methods disclose how to store not-usable electricity in the form of thermal energy and how to retrieve the thermal energy stored, efficiently. Once the thermal energy is retrieved, a conventional method of generating electricity from heat, such as a steam blower driving a steam turbine can be used to generate usable electricity. The same methods can be used to store even usable electricity, when not needed by the current demand, for an on-demand later use.
Latent heat can be produced by a phase change material (PCM). The use of a PCM, for thermal energy storage and retrieval, provides the advantages of (i) high energy density and (ii) isothermal behavior during thermal charging and discharging. In prior art, thermal energy storage systems utilize heat exchangers, submerged in a PCM for adding and removing thermal energy. It is well known in the art that removal of thermal energy from a PCM material, such as a nitrate salt, causes the salt to solidify on the heat exchanger surfaces. Such PCM materials have very low thermal conductivity when in solid phase. Therefore, when a PCM solidifies on a heat exchanger surface, during a thermal energy retrieval cycle (discharge), it lowers the thermal conductivity factor drastically. Since the heat transfer rate to a substance is directly proportional to the surface area of the substance and the thermal conductivity factor, the heat power transfer rate declines critically, deteriorating the heat exchanger's effectiveness substantially. Therefore, there is a need for a method to provide an efficient retrieval of thermal energy stored in a PCM by a prime source of electricity such as a not-usable source of electricity initially produced by a renewable source. Since these methods, disclosed herein, are capable of handling a source of not-usable electricity, it is easy to understand that they can also handle usable electricity as well.